This invention relates to the field of electric wave filters usable in power supply apparatus having a combination of pulsating load currents and limited supply currents. The described invention is particularly useful in satellite and other weight and volume limited environments.
Electrical energy storage in capacitor elements such as the common electrolytic capacitor frequency achieves an energy storage density in the order of 1 joule per pound of capacitor weight. For many presently feasible space shuttle and military space missions, this storage density in an electrical filter element provides a severe limitation as to the type of space mission that can be undertaken.
By way of example, the first man-made satellite, the Russian Sputnik launched in the late 1950's, employed a modest battery-powered electrical system which was capable of operating the satellite for a few weeks of time, but which nevertheless accounted for over one third of the satellite's overall weight. In the intervening twenty-five-plus years, launchable payloads have increased significantly in size, and improved space energy sources have become available. Even with present technology, however, the use of satellite systems having power supplies in range of 50 kilowatts (KW) is limited to low earth orbit because of the inability to transport systems of this electrical size and weight into higher orbit. A significant improvement in power supply weight will therefore contribute noticeable to the ability to place systems of this power level in higher orbit and enable the achievement of proposed systems having electrical capabilities in excess of 100 kw.
Electrical filtering is a necessary component in these larger power supplies as well as in power supplies of more modest capability. Electrical filters including energy storage capacitor elements are necessary, for example, in power supply waveform correcting, energy storage between pulses from an energy source, energy storage or buildup between high energy dumping events as might occur in a pulsed laser weapon, for example, and possibly for energy storage during the non-illuminated portion of a dark/light solar exposure cycle.
Under certain conditions as described subsequently herein, it is feasible to provide up to a tenfold increase in power supply energy filter storage density over the values described above using a different approach from that of the common electrolyte capacitor. In some proposed high-energy satellite applications, energy storage improvements of this capability would, for example, provide a satellite weight savings in the range of two to three tons of system payload. A central portion of this improvement resides in an optimized application of a rechargeable or secondary battery such as the nickel cadmium battery as an energy storing electrical filter element. In addition to the indicated considerations of energy storage density, such factors as battery service life, the imposed depth of discharge and the physical properties of battery filter cells require attention in embodying an electrical filter having these improved characteristics.
The patent art discloses several examples of battery cells usable for meeting a variety of battery requirements and their manufacture. Included in this art is the patent of Brijesh Vyas, U.S. Pat. No. 4,471,038, which concerns an alkaline battery cell, preferably a nickel-cadmium cell, which is improved through the addition of organic polymer compounds to one of the cell electrodes.
The patent art of interest also includes the patent of Margaret A. Reid, U.S. Pat. No. 4,439,465, which concerns a method for making a lightweight battery substrate or plaque that is also usable in a fuel cell.
The patent of Claude J. Menard, U.S. Pat. No. 4,154,908, concerns a electrode configuration for alkaline batteries wherein shapes enabling the use of unequal electrode material amounts on electrodes of different polarity are used--in order to obtain an improved life cycle and superior volumetric energy density. The Menard patent principally concerns silver-zinc, silver-cadmium, and nickel-zinc batteries. The Menard patent also teaches the use of potassium hydroxide as an electrolyte, and is concerned with increasing the number of discharge cycles and the depth of discharge characteristics of a battery. The Menard patent is especially concerned with electrode shape change or the migration of active material between different regions of an electrode.
The patent of Gunter Gutmann, U.S. Pat. No. 4,215,184 concerns an improved arrangement for nickel-oxide/hydrogen battery cells which achieves improved heat transfer in the axial direction of the cell through a reduction of the number of stacked elements in a cell.
The patent of David H. Fritts et al, U.S. Pat. No. 4,242,179, concerns a method for fabricating cadmium electrodes usable in nickel-cadmium and silver-cadmium batteries, for example. The Fritts patent achieves an improved loading of the cadmium material without surface buildup and also eliminates some of the electrode processing steps previously required.